The present invention is related to, and claims priority from, Swedish Patent Application No. 9904154-3, filed Nov. 17, 1999, the entire contents of which are hereby incorporated by reference in its entirety for all purposes.
The present invention relates generally to an antenna device and more particularly to a combined antenna device including an internal global positioning system (GPS) antenna and at least one internal antenna for cellular radio communication.
The use of a Global Positioning System(GPS)for determining the position of a terminal (such as a mobile phone) is increasing. GPS typically uses electromagnetic waves with circular polarization and a center frequency of 1.575 GHz. Today, the terminal is often a dedicated GPS terminal with an antenna arrangement adapted for GPS communication. The antenna is often a patch or quadrifilar helical antenna.
However, these types of antennas occupy a large space, especially the helical antenna. Also, a patch antenna has a considerable extension in two dimensions, making it difficult to place on a small substrate. It also requires a ground plane separated from the patch and being larger than the patch element.
The use of mobile phones and multi-purpose communication devices is increasing. Among the cellular mobile phone systems in use today can be mentioned the GSM system, using linearly polarized electromagnetic waves belonging to frequency bands of 900, 1800 or 1900 MHz, and the CDMA, JPC and AMPS systems.
There is a desire to integrate the functions of the GPS and the mobile phone systems into one terminal, i.e., a hand-portable radio communication device with a GPS function as well. However, the competing desire to make mobile phones compact poses special problems when designing the antenna arrangement adapted for use with both systems.
It is known antenna arrangements including a vehicle antenna for satellite navigation and for mobile radio communication. In one conventional device an arrangement including both a GPS antenna and an antenna working in the GSM bands. However, this arrangement is a flat-topped antenna apparatus intended for arrangement on a conducting surface. The radiating and receiving elements of the different antennas are arranged essentially parallel to each other and in different planes.
In another conventional device a radio communication device including a conventional cellular antenna and a GPS antenna in the form of a helical antenna are placed in an elongated antenna holder resembling a conventional rod antenna. The helical antenna is spaced apart from the terminal body by a communicating section in the antenna holder. Alternatively, this device uses a patch-like antenna element in the upper part of the terminal body mounted on a flat substrate. On the underside of the substrate is a ground plane for the patch-like antenna element. This configuration is not suited for use with a portable radio communication device, such as a mobile phone, due to its space-demanding configuration.
What is needed, therefore, is an antenna device for use in a terminal that overcomes the shortcomings of conventional devices described above.
The present invention is therefore directed to an antenna device, a communication device including the antenna device and a method of operating and the communication device that substantially overcomes one or more of the problems due to the limitations and disadvantages noted above.
An object of the present invention is to provide a compact antenna device including both an antenna for circularly polarized electromagnetic waves, such as for the GPS system, and at least one antenna for linearly polarized electromagnetic waves, such as for cellular mobile telephone systems.
Another object is to provide a radio communication device incorporating an antenna arrangement operating both with linearly and circularly polarized radio signals.
Still another object is to provide a method of operating a portable radio communication device having a first and a second antenna element.
The invention is based on the realization that an elongated element can be used as an antenna for receiving circularly polarized electromagnetic waves, such as those used in the GPS system, and that a common ground plane can be used for antennas operating with different kinds of polarization.
To achieve the above and other objects, an antenna device disposed in a terminal is disclosed, having a first antenna element adapted to transmit and receive electromagnetic waves and second antenna element adapted to receive circularly polarized radio signals.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.